1. Field of the Invention
This invention relates to a non-aqueous electrolyte cell, and more particularly, it pertains an organic electrolyte cell comprising a light metal as negative active material; a positive mass comprising manganese dioxide powder, carbon powder and optionally binder powder; and an organic electrolyte consisting of a solution of an inorganic salt of a metal corresponding to the light metal used as the negative active material in an organic solvent.
2. Description of Prior Art
Since an aqueous electrolyte cannot be used in a cell in which a light metal such as lithium, sodium or the like is used as negative active material, a non-aqueous electrolyte, namely a solution of an inorganic salt in an organic solvent is used. As the organic solvent, there is mainly used propylene carbonate, ethylene carbonate, tetrahydrofuran, acetonitrile or the like, and as the inorganic salt, there is used perchlorate, borofluoride or the like of lithium, sodium or the like. As the positive active material, there is used a metal oxide, halide, perchlorate or the like, among which manganese dioxide is preferable because when it is used as the positive active material, the discharge voltage is flat in relation to the discharge time, and the manganese dioxide is more stable against the organic electrolyte and lower in cost than the others. Accordingly, manganese dioxide is an excellent positive active material. Manganese dioxide has a resistivity of 3.5.times.10.sup.2 to 4.2.times.10.sup.3 ohm.cm, and hence, the electrical conductivity thereof is low. Thus, when manganese dioxide is used as the positive active material, it is necessary to blend therewith an electrically conductive material and if necessary a binder for bonding the two (Japanese Pat. No. 25,571/74). As the electrically conductive material, there is used a metal powder or carbon powder, and in order to make the weight of cell light and reduce the cost of cell, carbon powder is preferred. As the binder, there should be used a material stable against the organic electrolyte, and polytetrafluoroethylene is preferred. In order for a cell to have a high efficiency, it is ideal that the manganese dioxide used as the positive active material is completely consumed for the electrochemical reaction during the discharge, but in conventional cells, the utilization of manganese dioxide is only about 70%.
As a result of extensive research, the present inventors have unexpectedly found that the low utilization of manganese dioxide in conventional cells results from large particle size of manganese dioxide powder used and also large particle sizes of carbon powder and binder blended with the manganese dioxide powder. In the conventional cells, the average particle sizes of the three powders are more than 40 .mu.m, more than 15 .mu.m and more than 10 .mu.m, respectively. The present inventors have found that there is the upper limit as to the average particle sizes for obtaining a utilization of manganese dioxide of more than 93%.